Ceramic dielectrics



NOV. 14, 1967 5H|NQBU FUJ|WARA ET AL 3,352,697'

CERAMIC DIELECTRICS Filed May 12, 1964 (wa. m

. INVENTORS Y www United States Patent O 3,352,697 CERAMIC DIELECTRI'CSShinobu Fujiwara, Minami-Akita-gun, Akita-ken, Shigekazu Hayashi, Tokyo,and Kiyoto Kawakami, Nikahomachi, Yuri-gen, Akita-ken, Japan, assignorsto TDK Electronics Co., Ltd., Tokyo, Japan Filed May 12, 1964, Ser. No.366,765 3 Claims. (Cl. 106-39) ABSTRACT OF THE DSCLOSURE Ceramicdielectric materials are provided which consist of a sintered mixture of20 to 90% by weight of presintered SrTiO3, 3 to 60% by weight of Bi203and 5 to 60% by weight of TiOz.

The present invention relates to ceramic dielectrics with highdielectric constants and small temperature coeicients of dielectricconstants.

The object of the present invention is to provide ceramic dielectricswith high and fairly constant dielectric constants over a normaltemperature region and high Q- values for the elements of variouselectronic circuits.

As well known, BaTiO3 has been most widely used for practical purposesas a material having high dielectric constant. Nevertheless, due to thefact that the temperature coelicient of dielectric constant of bariumtitanate shows its maximum at about 120 C. and variation of its capacitydepends highly on temperature, the applications were highly limited forpractical purposes. Other dielectric materials with high dielectricconstants so far used show as large temperature coeicients as bariumtitanate (BaTiOs), and besides, they are unsatisfactory because of lowQ-values.

The present invention provides dielectric materials with improvedproperties which have been found unsatisfactory in the materials so farused; ceramic dielectrics with' high dielectric constant and smalltemperature coefficients are successfully produced from mixturescomprising mainly strontium titanate (SrTiO3), dibismuth trioxide(Bi203) and titanic oxide (TiOZ).

The ceramic dielectrics of the present invention are prepared in thefollowing manner: After pre-sintering, strontium titanate (SrTiO3) ispowdered and mixed with dibismuth trioxide (Bi-203) and titanic oxide(TiOZ), then the mixture is shaped under pressure followed by sinteringat a temperature higher than 1000 C. In the present invention,degeneration of the properties of the materials during storage betweenprocesses, e.g. by absorbing moisture, can be prevented by pre-sinteringthe strontium titanate (SrTiOS), which helps to attain the object of thepresent invention effectively.

The ternary diagram in the accompanying drawing shows the relationsbetween the three components of the products that is, strontiumtitanate, dibismuth trioxide and titanic oxide (SrTiO3, Bi2O3, and TiO2)and dielectric constants, its temperature coeicient and Q-value. Thethree numerical values at each point of composition represent dielectricconstant, its temperature coeilicient and Q- value respectively, goingfrom above to below, and these properties were measured at the frequencyof 1 mc./s.

In the present invention, to obtain the materials having desiredproperties, it is required, as can be seen from the diagram, theproportions of the three components of the products are limited asfollows:

Percentage by Component: weight SrTiO3 20-90 3,352,697 Patented Nov. 14,1967 Percentage by Component-Continued weight Bi203 3-60 TiO2 5-60 Thereasons for limiting the proportions to the said values are: when theproportion of strontium titanate (SrTiO3) is under 20 or over 90% byweight, dielectric constants become too low and their temperaturecoeicients do not indicate practically available values. When theproportion of dibismuth trioxide (Bi-203) is under 3 by weight,dielectric constants and temperature coeicients deviate from the desiredvalues, and when it exceeds 60%, Q-values become too low and theproducts are extremely When the proportion of titanic oxide (TiOz) isunder 5% by weight, temperature coeicients of dielectric constantsAbecome too large and Q-values-too small, and when it is over 60%,dielectric constants become too low and at the same time, the productsbecome porous.

The following examples will give a closer insight into the presentinvention.

Example I Pre-sinter strontium titanate (SrTiO3) at 1320 C., then grindit into powder, add dibismuth trioxide (Bi203) and titanic oxide (TiOZ)to it in the Weight proportion of and after shaping the mixture underpressure, sinter it at 1360" C. The ceramic dielectrics thus obtainedshow the following properties:

Dielectric constant 1100 Temperature coelicient of dielectric constant-2400 10*6/ C. Q-value 1000 Example 2 After pre-sintering at 1300 C.,strontium titanate (SrTiO3) is powdered and mixed with dibismuthtrioxide (Bi203) and titanic oxide (TiO2) in the weight proportion ofSrTiO3 :Bi2O3 :TiO2= 22 5 8 20 and after shaping under pressure, themixture is sintered at 1260 C. The products thus obtained show thefollowing properties:

Dielectric constant 278 Temperature coeicient of dielectric constant +30106/ C. Q-value Example 3 After pre-sintering at 1300 C., strontiumtitanate (SrTiO3) is powdered and mixed with dibismuth trioxide (Bi203)and titanic oxide (TOZ) in the weight proportion of SrTiOazBizOa:TiO2=90:5 :5

and after shaping under pressure, the mixture is sintered at 1380 C. Theproperties of the resultant products are:

Dielectric constant 577 Temperature coefficient of dielectric constant-3570 106/ C. Q-value 5000 Example 4 Strontium titanate (SrTiO3) ispre-sintered at 1300 C., then powdered and mixed with dibismuth trioxide(Bi203) and titanic oxide (TiOz) in the following proportion by weight:

SITlOa:Bl203TlO2=-`30Z20l50 and after the mixture is shaped underpressure, it is sin- 3 tered at 1280* C. The resultant products show thefollowing properLiesL Dielectric constant 195 Temperature coecient ofdielectric constant *1275 10-6/ C. Q-value 600 Example 5 Afterpresintering at 1300 C., strontium titanate (SrTiO3) is powdered andmixed with dibismuth trioxide .(Bi2O3) and titanic oxide (TiO2) in theweight proportion of SrTiO3:BiO2:TiO2=41:39:20

and after shaping under pressure, the mixture issintered at 1330 C. Theproducts thus obtained show the following properties:

Dielectric constant 342 Temperature coefficient of dielectric constant-872 10-6/ C.

Q-value 146 We claim:

1. Ceramic dielectric consisting of a sintered mixture of SrTiO3, BiZO?`and Ti02 in the weight proportion srTi03:Bi2o3;'rio2=22:58:20.

2. Ceramic dielectric consisting of a sintered mixture of Sr1`iO3,`Bi203 and TiO2 in then weight proportion SrTiO3:Bi2O3:Ti02=30:20:50.

3. Ceramic dielectric consisting of a sintered mixture of SrTiO3, Bi203and Ti02 in the Weight proportion 10 SrTiO3:Bi2O3:TiO2:41:39:20.

References Cited UNITED STATES PATENTS 3,074,804 l/l963 Planer 106-393,179,525 4/1965 Welsby et al. 106-39 FOREIGN PATENTS 1,178,181 6/1957France.

20 HELEN M. MCCARTHY, Prz'maly Examiner.

1. CERAMIC DIELECTRIC CONSISTING OF A SINTERED MIXTURE OF SRTIO3, BI2O3AND TIO2 IN THE WEIGHT PROPORTION SRTIO3:BI2O3:TIO2=22:58:20.